Current techniques for repair and/or regeneration of articular lesions (autogenous chondrocyte transplantation and mosaicplasty) are generally considered to be unsatisfactory due to the fact that they require the harvesting of healthy tissue. As such, research has focused on the development of engineered devices that have the ability to stimulate conduction of hyaline-like tissue into the treated regions without using autogenous tissue sources. Such devices would be considered optimized scaffolds.
In vivo studies of articular cartilage regeneration typically utilize one of two animal models: the osteochondral defect and the full-thickness chondral defect. The osteochondral defect model is ideal for the generation of cartilage neotissue because access to the traumatized bone bed allows for recruitment of precursor cells, thereby enhancing the intrinsic wound healing response. In fact, osteochondral defects in the non-load-bearing areas heal spontaneously, albeit with fibrous tissue. The load-bearing region, however, is known to not heal spontaneously, and is characteristically accompanied by resorption of osseous walls and the formation of cavitary lesions.
In cases where load-bearing surfaces have been investigated with good outcomes, care has been taken not to compromise the subchondral plate (e.g. full-thickness chondral defect model). However, because the chondral defect model does not generate a hematopoietic wound healing response, spontaneous regeneration does not occur and thus cellular therapies are usually used in such circumstances. One notable exception is mosaicplasty. Mosaicplasty in femoral condyle (osteochondral) defects has been shown to maintain subchondral bone structure, further indicating that application of physiologic force plays a role in maintaining subchondral bone integrity.
Particularly, mosaicplasty utilizes cartilaginous plugs, but due to the need to harvest tissue from other sites, this technique is sometimes viewed as being suboptimal. Therefore, research has focused on the use of implant devices. In published U.S. patent application 2001/0039455A1, prosthetic bio-compatible polyurethane plugs that mimic the materials properties of the adjacent bone or cartilage tissue layer are described. These implants are intended to fill a cartilaginous defect with a non-resorbable cartilage-like material. However, application of load to subchondral bone is not described.
The use of load during cartilage regeneration has been described in several publications. In U.S. Pat. No. 6,530,956 a resorbable cage-like scaffold is described that consists of high porosity material seeded with transplanted chondrocytes. Loading is discussed with respect to the cage-like scaffold for withstanding and resisting compressive forces so that cell growing compartments of the cage-like scaffold are protected during tissue regeneration.
U.S. Pat. No. 6,511,511 describes a fiber-reinforced, porous, biodegradable implant in which the fibers act like struts to provide strength and stiffness to the scaffold and provide support for physiological loads. One particular embodiment is for osteochondral defects. Loading, however, is discussed only with respect to the device resisting high compressive stresses in the defect region thereby protecting the implant during tissue regeneration. In a similar manner, U.S. published U.S. patent application 2002/0119177 describes a method for reinforcing the mechanical and handling properties of a resorbable foam matrix using a mesh-like fabric. The primary purpose of the reinforcing mesh is to maintain the integrity of the foam component for surgical handling.
In published U.S. patent application 2003/0108587, an implantable device is described that can induce compression, tension, shear and other biomechanical forces to cells in order to induce cell proliferation and thus wound healing. The device is essentially a bioreactor that exerts micromechanical stimulation to cells through materials properties or application of external forces. This is taught, however, with respect to the regeneration of cartilage and not with respect to the healing of the subchondral bone as in the present invention.
Thus the need exists for a device for regeneration of articular cartilage that simultaneously applies load to subchondral bone.
It is thus an object of the present invention to provide an implant for cartilage regeneration in load-bearing regions.
It is thus another object of the present invention to provide an implant that applies a load from an articulating surface of a bone platform to an area of subchondral bone.
It is yet another object of the present invention to provide a load bearing implant for that reduces subchondral bone resorption.